Method of producing glass in a flame

ABSTRACT

A method of producing a glass body composed of two or more oxides by the flame hydrolysis technique, for example incorporating an additive or dopant oxide in a fused silica glass body. The method comprises forming a gas stream containing vapors of a compound that will hydrolyze to a glass forming oxide, e.g., silicon tetrachloride (SiCl4), nebulizing an oxide forming compound or solution of such compound to form a mist in the nature of an aerosol, and simultaneously directing the mist and gas stream into a flame of combustible gas to form and codeposit a mixture of oxides corresponding to the vaporized and nebulized compounds.

United States Patent 1 Randall 1 METHOD OF PRODUCING GLASS [N A FLAME[75] Inventor: Eric N. Randall, Bath, NY.

[73] Assignee: Corning Glass Works, Corning,

[22] Filed: Jan. 11, 1974 [21] Appl. No: 432,573

[52] 0.8. CI. 65/18; 65/21; 65/120; 65/DIG. 16; 117/46 FS; 117/106 R [51] Int. Cl. C03b 23/20; C03c 7/00; C03b 25/00 [58] Field of Search65/18, 21, D1G,7, 33, 65/120. DIG. 16; 117/46 FS. 106 R, 105.2

[56] References Cited UNITED STATES PATENTS 2,967,113 1/1961 Liebahfskyet a1 117/106 R 2,993,809 7/1961 Bueche et a1. 117/106 R 3,535,89010/1970 Hansen et a1. 65/18 3,642.52! 2/1972 Moltzah et a1 11 117/1052Nebulizer Solution of dopont l 11 3,883,336 1 1 May 13, 1975 M.Peterson; Clarence R. Patty, Jr.

[57] ABSTRACT A method of producing a glass body composed of two or moreoxides by the flame hydrolysis technique, for example incorporating anadditive or dopant oxide in a fused silica glass body. The methodcomprises forming a gas stream containing vapors of a compound that willhydrolyze to a glass forming oxide, e.g., silicon tetrachloride (SiClnebulizing an oxide forming compound or solution of such compound toform a mist in the nature of an aerosol, and simultaneously directingthe mist and gas stream into a flame of combustible gas to form andcodeposit a mixture of oxides corresponding to the vaporized andnebulized compounds.

l0 Claims, 1 Drawing Figure Nebulizer Burner Aerosol Solution of dopontMETHOD OF PRODUCING GLASS IN A FLAME U.S. Pat. No. 2,272,342, grantedFeb. 10, l942 to J. F. Hyde, describes the flame hydrolysis technique ofproducing glass with reference to the production of pure fused silica,that is a glass composed entirely of sila ica (SiO As described by Hyde,a stream of gas carrying a hydrolyzable compound of silicon in vaporform is introduced into a flame of combustible gas. The compound ofsilicon is hydrolyzed in the flame to form amorphous silica which may becollected in particulate form, or may be deposited on a mandrel or othersupport as a preform. The preform may be vitrified in position, or maybe consolidated and vitrified by a separate heat treatment.

Subsequent patents, including U.S. Pat. No. 2,326,059 granted Aug. 3,1943 to M. E. Nordberg, and U.S. Pat. No. 2,239,551 granted Apr. 22,1941 to R. H. Dalton et al., describe methods of producing glasses byflame hydrolysis wherein the glass is composed of an oxide mixture, inparticular a fused silica type glass incorporating small amounts of oneor more additional oxides such as titania or alumina. In general, thesemethods involve forming a mixture of volatile compounds in the desiredproportions in a stream of gas fed to a combustion burner. The mixtureof vapors is then hydrolyzed to deposit a glass or preform containing acorresponding oxide mixture.

The mixed oxide glasses that can be produced by these earlier methodsare limited by the ability to obtain materials that are relativelyvolatile and that may be hydrolyzed and decomposed in accordance withthe flame hydrolysis technique. Even when suitable volatile compoundsare available, it is often difficult to control proportions in the finalproduct.

A copending application, Ser. No. 208,168 filed Dec. 15, 1971 in thenames of P. C. Schultz and F. W. Voorhees now U.S. Pat. No. 3,801 ,294,describes a modified vapor generating procedure wherein a carrier gas ispassed through a heated fluidized bed or layer of a particulate materialto entrain vapors of the material. My application, Ser. No. 432,572,filed of even date herewith and also entitled Method of ProducingGlass," discloses a method wherein particles of a finely dividedmaterial are entrained in a carrier gas and the oxide thereof iscodeposited with an oxide produced from a hydrolyzed vapor. Likewise,copending application, Ser. No. 407,918 filed in the name of P. C.Schultz and entitled Method of Producing Glass by Flame Hydrolysis,discloses a method wherein a porous preform, of the nature described byHyde, is impregnated in part at least to introduce a desired oxide. Eachof these methods has certain advantages, but no one of them provides thecapability of precisely varying and controlling composition to thedegree required in producing certain optical type products. It is thepurpose of the present invention to meet this need.

The present invention provides a completely novel approach to theproblem of producing by flame hydrolysis glasses that are composed of amixture of oxides, in particular a fused silica type glass containingone or more additive oxides. Further, it provides a convenient means ofintroducing such additives in a uniform manner and in controlled amount.The invention is based on my discovery that the flame hydrolysisprocedure can be applied to a mixture of hydrolyzable vapors andncbulized liquid, to produce a mixed oxide preform or glass and therebyachieve the desired purposes.

The invention is a method of producing by flame hydrolysis a glass bodycomposed of two or more constituent oxides which comprises forming a gasstream containing vapors of a compound that will hydrolyze to a glassforming oxide in a combustion flame, nebulizing a liquid to form anaerosol, the liquid being an oxide forming compound or solution of suchcompound, and simultaneously passing the vapor stream and the aerosolinto a combustion flame to form and codeposit a uniform mixture ofoxides corresponding, respectively to the vaporized and the ncbulizedmaterials. A specific embodiment of the invention provides a method ofproducing a fused silica glass body by the flame hydrolysis techniquewherein the glass contains at least one additive or dopant oxide.

The invention is of particular interest in, and hence is described indetail with respect to, the production of modified or doped fused silicatype glass bodies. However, it will be understood that the invention isnot limited to this type of glass, but may be employed as well in theproduction of glasses based on other glass forming oxides. For example,a germanium oxide (GeO type glass body may be produced by mixing vaporsof germanium chloride (GeCh) with a suitable material that isconvertible to the corresponding oxide. It will also be apparent thatother types of fused oxide glasses, such as B 0 P 0 and Se0 glasses, maybe produced by suitable selection of materials.

In practicing the invention, a gas stream is provided containing thevapors of at least one material that will hydrolyze to an oxide in acombustion flame. The vaporizable material may be any of the metalhalides, metal organics, or other compounds that are suitable for theconventional flame hydrolysis process of glass production. The selectedmaterial may be volatilized in conventional manner, for example byheating in a water bath and/or entrainment by a carrier gas. Alternativeprocedures involving generation of vapors from a fluidized bed aredescribed in copending application, Ser. No. 208,168, mentioned earlier.

Simultaneously, a second material, thermally convertible or decomposableto a stable oxide, is ncbulized to form a mist. This mist is composed ofcolloidal size droplets and is in the nature of an aerosol. The materialemployed may be a liquid itself, such as a liquid organometalliccompound. Alternatively, it may be an aqueous or nomaqueous solution ofany suitable compound. For example, acetates, nitrates, hydroxides,oxides and halides of sodium, lead, cobalt, barium, aluminum and boronhave been employed to produce additive oxides in fused silica glasses.

The basic requirement is that a liquid be converted to extremely smallsize droplets that will produce oxide particles having a size in thesame magnitude as that of the silica particles formed by flamehydrolysis. 1n general, the particles formed should not exceed 1 micronin size and preferably are less than 5% micron. Larger particles fail tocompletely combine with the basic glass former, e.g. silica, and tend toproduce solid inclusions in the glass. To this end then, it is desirablethat the droplets in the aerosol be relatively uniform in size and notexceed about ten microns.

It is possible to achieve the requisite small droplet size with ordinaryspray equipment. However, such a spray usually lacks uniformity andcontains a sufficient number of large droplets so that inclusions occurin the resulting glass.

It has now been found that the desired uniformity of small droplet sizecan be achieved by a practice known as impaction. In usual spraypractice, an aspirated stream of large droplets is split into smallerdroplets. In contrast, the impaction practice involves directing anaspirated stream under pressure against a surface, for example a body ofthe liquid being dispersed, to effectively shatter large droplets intonumerous small droplets. Commercial devices for carrying out thisprocess are available as referred to later.

An alternative is described in the May, 1973 issue of Popular Science,pp. 102-104, 162, 164. This procedure involves flowing a thin film ofliquid over a spherical surface, and disrupting the flim with acountercurrent of air to nebulize the liquid,

The vapor stream and the aerosol may be passed through separate burners,or the aerosol may be directed into the flame in which the siliconcompound, or other glass former, is being hydrolyzed. The turbulence ofthe flame results in homogeneous intermingling and codeposition of theoxides formed.

The vitrified oxide particles formed may be deposited as a non-porousglass boule in accordance with conventional manufacturing practice.Alternatively, they may be deposited, at a somewhat lower temperature,as a porous preform on a suitable support or mandrel. Com positionalcontrol of the oxide mixture produced is achieved in part by controllingthe flow rates of the two gas streams, and thereby the relativeproportions of the vapor material and aerosol introduced into the flamevAs explained later, flame temperature and position are also significantfactors.

If the oxide mixture is deposited in a dense sintered form, commonlyreferred to as a preform, this preform may be given a subsequent heattreatment which consolidates the porous body into a non'porous vitreousbody. This consolidating heat treatment may be an overall heating of thepreform body as disclosed in the patents mentioned above. Alternatively,the heat treating process described in application Ser. No. 239,742,entitled Method and Apparatus for Producing High Quality Fused Silica"and filed Marv 30, 1972 in the names of J. S. Flamenbaum et al. now US.Pat. No. 3,806,570, may be employed. In accordance with the latterprocedure, the preform is subjected to a progressive heat treatment byslowly passing it into or through a thermal zone wherein consolidationtakes place. This process has the advantage of minimizing gas inclusionsin the body of the consolidated giass.

The invention is further described with particular reference to thepreferred embodiment (fused silica glasses) and to the accompanyingdrawing wherein the single figure is a schematic illustration of asimple apparatus for practice of the invention.

The drawing shows a stream of carrier gas (oxygen) being introduced froman external source (not shown) into a flask of silicon chloride (SiCl toproduce a stream of gas containing entrained silicon chloride vapors.This oxygen-vapor stream is passed into a combustion burner which isalso supplied with a gasoxygen mixture to form a flame. The SiCl, ishydrolyzed in such flame to form minute particles of silica. These particles may be collected in particulate form, as a preform composed ofcoherent particles, or as a glassy boule, in accordance with proceduresknown in the art.

This portion of the drawing illustrates conventional practice asdescribed in the patents mentioned earlier.

Any suitably volatile silicon compound, such as any of the halides, asilane, or a halogen derivative thereof, might be substituted in theflask to provide vapors in the carrier gas stream. The chloride isparticularly suitable because it is readily volatilized. If desired, thechloride, or other liquid, may be heated in a water bath for fasterevolution of vapors. Those familiar with this art will of course readilyappreciate that other volatile compounds that undergo a suitabletransformation, e.g. germanium chloride, might be substituted for theSiCl shown.

In accordance with the present invention, a stream of liquid (shown as asolution of dopant") is aspirated by air pressure from a container intoa nebulizer which converts the liquid into an aerosol as describedearlier. The nebulizer may for example be a simple arrangement whereinaspirated liquid is forcefully directed against the liquid surface in acontainer to form the desired aerosol.

Alternatively, an impaction device, supplied by Sonic DevelopmentCorporation under Code No. 52H and described in their Bulletin S-l00,may be employed. Likewise, a thin film nebulizer, as described earlier,might be employed. In any case, the aerosol is directed toward thecombustion flame of the burner in which SiCl is converted to silica.Thus the two oxides form within the flame, are intermingled by theturbulence, and are codeposited therefrom.

The invention is further illustrated by several specific examples of itspractice with reference to the drawing.

EXAMPLE I Cobalt chloride (CoCl was dissolved in methanol to provide 3liters of 0.1 M solution. This solution was placed in a reservoir fromwhich it was aspirated into a nebulizer in the form of an impactionnozzle. This nozzle is specially designed to produce an aerosol byimpaction of a liquid stream within a metal cap. The nozzle may beadjusted to produce aerosols with droplet sizes ranging from submicronup to about ten microns.

The methanolic solution of cobalt chloride was thus nebulized at a rateof 66 cc/minute to form an aerosol. This was fed as a cone-shaped mistinto the flame of a burner supplied with natural gas at 0.4 cubic feetper minute (cfm) and oxygen at 0.35 cfm. A stream of gas and vapor wassimultaneously produced by bubbling oxygen at a rate of 2,800 cc/minutethrough a container of liquid SiCl at 25C. This stream was passedthrough the burner and into the flame thereof simultaneously with theCoCl solution. The SiCl, vapors hy drolyzed to SiO while the methanolburned and the CoCl converted to cobalt oxide (C00). The oxides mixed inthe turbulence of the flame to form a uniform dispersion of C00 insilica which was deposited on a mandrel to form a preform.

The mandrel was a five (5) mm. o.d. fused quartz tube 6 inches in lengthattached to a inch diameter handle. The mandrel was rotated at rpm whilebeing translated in a reciprocating manner at 16 inches per minute andat a distance of seven inches from the flame.

An even coating of the two oxides was deposited for a period of aboutone hour. The resulting preform was removed and slowly lowered throughthe hot zone (l,450C.) of a helium atmosphere induction furnace at arate of 25 inches per hour. The resulting glass body was pale blue,transparent, and contained 4 p.p.m. CoO as determined by massspectographic analysis.

EXAMPLE ll A 0.05 M solution of chromium trioxide (CrO was aspirated andnebulized by the system of Example I from a container pressurized at 4psig. and providing a solution flow rate of about 2 liters/hour. Theoutlet of the aspirator assembly was positioned inches from and directedtoward a burner flame as in Example I, whereby a cone shaped mass ofaerosol was directed into the flame.

The burner flame was fed by an oxygen stream at 032 cfm and natural gasat 027 cfm. A gas-vapor stream was produced by passing oxygen at a rateof 2,800 cc/minute through SiCl, liquid at 25C. and was fed through theburner into the flame.

The resulting oxide mixture was collected, and the preform consolidatedto a glass, as in Example I. The glass was pale green, transparent, andshowed less than ten p.p.m. chromium oxide by spectrographic analysis.

EXAMPLE Ill The procedure of Example II was repeated with identicalconditions and materials, except that a 1.15 M solution of CrO wasemployed. The resulting glass was extremely dark green in color, showedsigns of devitrification occurring, and was found to contain 200 ppm. CrO EXAMPLE IV The procedure of Example ll was repeated with changes inboth conditions and materials. A 0.375 M solution of ammonium borate((NH,) B O-,) was aspirated and nebulized to form an aerosol. This wasdelivered to the burner, as previously, but at different distances from.he burner and under different tank pressures. In summary, the aerosolwas delivered, (l) at a distance of l8 inches and at a solution flowrate of 35 cc/minute, (2) at a distance of 19 inches and at a solutionflow rate of 50 cc/minute and (3) at a distance of 20 inches and at asolution flow rate of 66 cc/minute.

At the same time an oxygen-SiCl, vapor stream was delivered as before,but the distance of the burner nozzle from the bait upon which theoxides were deposited was varied in the three runs as (l) 7 /2 inches;(2) 6 inches, and (3) 6% inches.

The oxides were deposited and consolidated as before, producing clear,uncolored glass in each case. On analysis. the three glasses contained(1 6.8% B 0 (2) 3.8% 8 0 and (3) 5.2% B 0 This suggests that increasingthe borate flow rate, while increasing the B 0 produced, does not haveas much influence as varying the spacing of the SiO producing burnerfrom the bait.

EXAMPLES V AND VI Lead oxide (PbO) was introduced into fused silica asan additive using two different lead compounds. In each instance, a leadcompound solution was nebulized to form an aerosol with the impactionprocedure described in Example I.

In the first run, a 1.0 M aqueous solution of lead nitrate (Pb(NO wasnebulized and the aerosol directed at a burner flame from a nozzlepositioned 43 inches from the flame, the solution being consumed at aflow rate of 70 cc/minute. Simultaneously, SiCl. va pors were deliveredto the oxy gas burner as in Example l with the burner nozzle 5 inchesfrom the fused quartz bait upon which the mixed oxides were depos ited.

In the second run, a 2.75 M solution of lead perchlorate (Pb(ClO wasnebulized and delivered as before with the nozzle positioned 42 inchesfrom the bait. The SiCl vapors were delivered as before, but the burnerwas positioned 5 H2 inches from the bait.

Subsequent glass analyses showed 150 p.p.m. PbO in the glass of thefirst run and 140 ppm. in the glass of the second run.

EXAMPLE Vil A further test was conducted to determine influence of flametemperature and burner position on oxide proportions. In this test a 0.5M solution of Pb(NO was nebulized at a rate of cc/minute and the aerosoldirected at a flame through a nozzle positioned 38 inches from theflame.

SiCl vapors were delivered, as previously, to a combustion burner.However the burner gas flows were reduced to 0.27 cfm gas and 0.30 cfmoxygen, thus providing a less intense and cooler combustion flame. Inturn, the burner nozzle was moved back to 6 inches from the bait uponwhich the oxides were being deposited.

The preform thus produced was consolidated, as previously, to a clearglass which, upon analysis showed 1.09% by weight lead oxide (PbO). Thisindicates the necessity for maintaining constant flame temperature andposition for consistent compositions. It also illustrates the manner inwhich these conditions may be varied to achieve compositionalvariations.

I claim:

1. A method for making a transparent, homogeneous glass body consistingof at least two constituent oxides comprising the steps:

a. entraining within a gas stream vapors of a compound of SiO GeO B 0 P0 and SeO that will hydrolyze in a flame to produce the correspondingglass forming oxide in particulate form;

b. nebulizing a solution containing a metal oxide or a metal compoundthermally convertible by heat treatment in a flame to a stable metaloxide into an aerosol consisting of substantially uniformly-sizeddroplets that do not exceed about [0 microns in diameter; and

c. simultaneously passing said vapors and said aerosol into the flame ofa combustion burner to form and codeposit a homogeneous oxide mixture asa glass body free from inclusions.

2. The method of claim 1 wherein said vapors consist of a siliconcompound.

3. The method of claim 1 wherein the aerosol is an aqueous saltsolution.

4. The method of claim 1 wherein both said vapors and said aerosol arepassed into the same flame.

5. The method of claim 1 wherein said vapors and said aerosol are passedinto separate flames.

6. A method for making a transparent, homogeneous glass body consistingof at least two constituent oxides comprising the steps:

a. entraining within a gas stream vapors of a compound of SiO (3e0 B 0 P0 and SeO that will hydrolyze in a flame to produce the corre spondingglass forming oxide in particulate form;

rous glass body free from inclusions by heat treatrn'ent thereof. 7. Themethod of claim 6 wherein said vapors consist of a silicon compound.

8. The method of claim 6 wherein the aerosol is an aqueous saltsolution.

9. The method of claim 6 wherein both said vapors and said aerosol arepassed into the same flame.

10. The method of claim 6 wherein said vapors and into separate flames.

said aerosol are passed t fi 1F

1. A METHOD FOR MAKING A TRANSPARENT, HOMOGENEOUS GLASS BODY CONSISTINGOF AT LEAST TWO CONSTITUENT OXIDES COMPRISING THE STEPS: A. ENTRAININGWITHIN A GAS STREAM VAPORS OF A COMPOUND OF SIO2, GEO2, B2O3, P2O5, ANDSEO2 THAT WILL HYDROLYZE IN A FLAME TO PRODUCE THE CORRESPONDING GLASSFORMING OXIDE IN PARTICULATE FORM; B. NEBULIZING A SOLUTION CONTAINING AMETAL OXIDE OR A METAL COMPOUND THERMALLY CONVERTIBLE BY HEAT TREATMENTIN A FLAME TO A STABLE METAL OXIDE INTO AN AEROSOL CONSISTING OFSUBSTANTIALLY UNIFORMLY-SIZED DROPLETS THAT DO NOT EXCEED ABOUT 10MICRONS IN DIAMETER; AND C. SIMULTANEOUSLY PASSING SAID VAPORS AND SAIDAEROSOL INTO THE FLAME OF A COMBUSTION BURNER TO FORM AND CODEPOSIT AHOMOGENEOUS OXIDE MIXTURE AS A GLASS BODY FREE FROM INCLUSIONS.
 2. Themethod of claim 1 wherein said vapors consist of a silicon compound. 3.The method of claim 1 wherein the aerosol is an aqueous salt solution.4. The method of claim 1 wherein both said vapors and said aerosol arepassed into the same flame.
 5. The method of claim 1 wherein said vaporsand said aerosol are passed into separate flames.
 6. A method for makinga transparent, homogeneous glass body consisting of at least twoconstituent oxides comprising the steps: a. entraining within a gasstream vapors of a compound of SiO2, GeO2, B2O3, P2O5, and SeO2 thatwill hydrolyze in a flame to produce the corresponding glass formingoxide in particulate form; b. nebulizing a solution containing a metaloxide or a metal compound thermally convertible by heat treatment in aflame to a stable metal oxide into an aerosol consisting ofsubstantially uniformly-sized droplets that do not exceed about 10microns in diameter; c. simultaneously passing said vapors and saidaerosol into the flame of a combustion burner to form and codeposit ahomogeneous oxide mixture as a porous preform; and then d. consolidatingsaid porous preform into a nonporous glass body free from inclusions byheat treatment thereof.
 7. The method of claim 6 wherein said vaporsconsist of a silicon compound.
 8. The method of claim 6 wherein theaerosol is an aqueous salt solution.
 9. The method of claim 6 whereinboth said vapors and said aerosol are passed into the same flame. 10.The method of claim 6 wherein said vapors and said aerosol are passedinto separate flames.